Frequently encountered while containing sodium chloride, sodium sulfate group of mixed solution containing wastewater in the salt chemical industry, chlor alkali chemical industry, coal chemical industry, hydrometallurgy, pharmaceutical and other industries. According to different conditions, usually take the following processing technology:
Sodium chloride and sodium sulfate mixed with sodium chloride by direct evaporation.
Second, the refrigeration denitration have sodium sulfate decahydrate, contains large amounts of sodium chloride and a small amount of sodium chloride mother liquor to electrolytic production of caustic soda, Glauber's salt melting evaporation of high purity anhydrous sodium sulfate.
Third, CO production of salt and Glauber salt, high temperature evaporation of sodium sulfate and low temperature evaporation mother liquor to sodium chloride, part of the mother liquor efflux; or high temperature to obtain sodium chloride, mother liquor evaporation under low temperature to obtain anhydrous sodium sulfate, part of the mother liquor row.
Fourth, CO production of salt and Glauber salt, high temperature evaporation of anhydrous sodium sulfate, freezing crystallization of sodium sulfate and sodium chloride dihydrate salt, salt melting return liquid evaporation ponds to get anhydrous sodium sulfate; sodium chloride crystals of high purity sodium chloride mother liquor evaporation, after centrifugation mother liquid part of the outer row.
In the process of selection, the first process is the most simple, but only get mixed salt, economic value is not high. The process is suitable for in addition to containing sodium chloride and sodium sulfate containing contains plenty of other effects of sodium chloride and sodium sulfate product purity of impurities, it is difficult to carry out effective separation conditions, in recent years, the chemical factory integrated with saline wastewater by the process are used in a wide range of applications.
The second process is relatively simple, can get high purity of Glauber's salt and separation of high purity sodium chloride solution, the process especially in sodium chloride and sodium sulfate content were higher in the condition, in chlor alkali industry is most widely used, many domestic Zhejiang Jiahua, Taishan salinization, Luxi Chemical Industry and other chlor alkali enterprises adopt the technology. Disadvantages of Glauber's salt storage and transportation is convenient, need hot melt re evaporation get anhydrous sodium sulfate, and mirabilite crystallization heat and heat of solution are larger and need to consume more cooling capacity and steam, energy consumption is relatively high.
Two of the third processes are evaporation process, the energy consumption is higher than the first, but it can effectively separate sodium chloride and sodium sulfate products. Also asked other impurity content is less, otherwise, it will deviate from the purity of the phase diagram area affect the final sodium chloride and sodium sulfate, the mother liquor displacement increases. The earlier process by the Swiss Sulzer public success and in the eighties the introduction of domestic, in Salt Lake chemical industry has been widely promoted and the Shanxi Nanfeng group first used in China, is a mature technology. In recent years, with the development of MVR evaporation and crystallization technology, low operating cost has been widely used in the process.
Fourth processes for evaporation, freezing, evaporation three processes, although the overall energy consumption is higher than the third, but can get a higher purity of anhydrous sodium sulfate and sodium chloride. Which both high temperature evaporation or low temperature evaporation section are very mature technology and freezing crystallization in the introduction of chlor alkali saline removal nitrate, lithium denitrification and other continuous freezing crystallization field has been widely used, such as Sichuan Tianqi lithium industries, Shanxi in Zaozhuang in Department of chemistry.
From the above analysis, we can see that each process has its own advantages and disadvantages, and it is also a very mature technology. Only need according to different conditions, the requirements of the appropriate choice of the most reasonable.